This is a resubmission of a previous proposal in which the researchers plan to design and construct a specialized near-infrared spectroscopy (NIRS) instrument for use in urological evaluation of male impotence. The instrument will be tested for its usefulness in the diagnosis of impotence arising from vascular causes. The thesis of the program is that the dynamics of blood volume changes in the penis can have diagnostic significance, and that determination of these changes by a simple spectrophotometric technique will have an impact on the treatment of vasculogenic impotence. To support this thesis, a modification of an existing near-infrared device will be made for studying the blood flow in the penis, and 20 normal volunteers and 40 volunteers with vasculogenic impotence will be studied.